Intraocular lenses may be used as surgical implants to replace the natural lens of the eye that has been removed to correct some vision impairment, for example cataracts. Intraocular lenses generally have two principal parts, a light focusing optic supported in a central position within the eye by means of haptic supports. There are a variety of lens designs available. The optic may be supported by plastic filaments which extend from the optic to the peripheral anatomy of the eye. Alternatively, the optic may be supported by solid haptics which are formed as an integral part of the optic. The type of lenses which use plastic support haptics are shown, for example, in U.S. Pat. No. 4,159,546. Lenses with solid support haptics are shown, for example, in U.S. Pat. No. 4,261,065.
The optic portion of the lens usually has an anterior and a posterior optical surface spaced axially apart from one another and a surrounding circumferential edge. The most commonly used optic has a convex anterior surface and a planar posterior surface. The majority of the light impinging on the eye is focused on the retina by a central optical portion of the lens surfaces. Surrounding this central portion is a peripheral transition zone which is between the central portion and the edge of the lens.
It will be appreciated that all surfaces of the intraocular lens should be smooth and rounded to avoid damaging the interior anatomy of the eye during intraocular lens implant surgery or during use of the lens after implantation. For lenses which are supported by plastic filaments the transition between the edges of the optic and the anterior and posterior optical surfaces should be smooth to avoid damaging the interior portions of the eye with which the edges may come in contact. For solid one-piece lenses, it is also important that the edges of the haptic supports also be rounded for the same purpose.
A variety of well-known polishing and cutting processes are used to smooth the rough edges of lenses. These processes can be expensive and time consuming. Lenses which are lathe cut from one piece of hard plastic can have their edges smoothed by tumbling in an abrasive medium. However, abrasive tumbling can change the geometric shape of the optical surfaces of the lens and, hence, the optical properties of the lens so that after tumbling the optical properties of each lens must be carefully checked. It would be desirable if a method and apparatus could be found for permitting the edges of intraocular lenses to be rounded by an abrasive tumbling process which would not require the careful verification of the fidelity of the optical properties of the lens.
It would also be desirable to have a fixture for holding the lens during a variety of processing steps to which a lens must be subjected. For molded optics, processing steps include removing molding gates and flash material that remains on the lens after molding, rounding the edges of the lens and drilling various positioning holes and haptic support holes. It would also be desirable to use one fixture in which a lens could be passed from one manufacturing station to another so that human handling of the optical portion of the lens could be reduced. Such a fixture would also facilitate automated manufacturing of intraocular lenses.